Liquid nonaqueous detergents are well known in the art. This class of detergents is particularly interesting for enhancing the chemical compatibility of detergent composition components, in particular bleach precursors and bleach sources.
In such nonaqueous products, these bleaching precursors are less reactive than if they had been dissolved in the liquid aqueous matrix.
One of the drawbacks of bleach precursors may be their low dissolution rate in the wash liquor. As a result, the perhydrolysis rate is reduced which in turn affects the cleaning performance. This problem is even more acute with the move in consumer washing habits towards lower temperature and shorter washcycle. Problems can also, in particular, be encountered when the said bleach precursors are used under high hardness conditions, resulting upon dissolution in the formation of calcium salts of low solubility. Such a problem of reduced perhydrolysis is further increased where the bleach precursor is present as certain divalent and/or trivalent metal salt as such a form exhibits a very low rate of dissolution, thus affecting the perhydrolysis rate.
A further problem, associated with the use of bleach precursors having slow perhydrolysis rates, appears when soiled fabrics release a catalase enzyme in the washing liquor. Hence, due to the slow perhydrolysis of the precursor, the catalase will destroy the hydrogen peroxide component before the bleach activator is properly perhydrolysed. As a result, the concentration of peracid present in the wash is reduced and so is the bleaching performance.
Another problem associated with the use of bleach precursors is that there is a tendency for such products to phase separate as dispersed insoluble solid particulate material drops from suspension and settles at the bottom of the container holding the liquid detergent product. Phase stabilizers such as thickeners or viscosity control agents can be added to such products to enhance the physical stability thereof. Such materials, however, can add cost and bulk to the product without contributing to the laundering/cleaning performance of such detergent compositions.
A further problem associated with bleach precursors is that it has been observed that bleach precursors can induce visual inhomogenities in the final product. This represents a problem as composition aesthetics is a key element in terms of consumer acceptance.
Accordingly, the formulator of a nonaqueous liquid detergent composition is faced with the challenge of formulating a physically stable non-aqueous detergent composition which provides effective dissolution of the precursor in order to result in an efficient perhydrolysis.
The Applicant has now surprisingly found that bleach precursor particles of reduced size within a liquid non-aqueous detergent composition do meet the above objectives.
It is therefore an advantage of the invention to provide bleach precursors containing non-aqueous liquid-detergent compositions which produce efficient rate of dissolution, which are physically stable and which have improved visual appearance.
It is a further advantage of the invention to provide compositions with improved resistance to a catalase enzyme.
It is another advantage of the invention to provide compositions which enable the use of a lower amount of peroxygen bleach.
EP 0 541 610 discloses the preparation of nonaqueous liquid detergents containing more than 8% anionic surfactants by wet grinding of a mixture comprising a peroxygen bleach. The average particle size obtained after grinding is in the preferred range of 1-5 microns. This document does not disclose or suggest that utilizing bleach precursor particles of reduced particle sizes does provide the benefit of the present invention.